Field of the Invention
The present invention relates to an image forming apparatus capable of transiting to a power saving state, and a control method.
Description of the Related Art
It is becoming popular that an image forming apparatus has a function of shifting to the power saving state when, for example, the user does not operate the image forming apparatus for a predetermined time, in terms of energy saving. Various arrangements for reducing power consumption in the power saving state have been considered. In an image forming apparatus described in Japanese Patent Laid-Open No. 2003-89254, power is supplied to a controller unit that can process and store image information in the standby state, and an input/output unit that receives/outputs information from/to a network. Further, Japanese Patent Laid-Open No. 2003-89254 describes that power supply to the controller unit is stopped in the power saving state and the input/output unit is caused to transmit/receive data to/from an external apparatus, in order to reduce power consumption in the power saving state.
However, when power supply to the controller unit is stopped in the power saving state, as in Japanese Patent Laid-Open No. 2003-89254, the following is considered to occur.
A network or facsimile apparatus (input/output unit) needs to send back a response within a specific time for a request (also called “an inquiry) from a communication partner device. This is because, for example, if the image forming apparatus does not send back a response within a specific time for a request from an SIP server, the connection is canceled. The specific time is, for example, 4 seconds depending on the type of the SIP server. When returning from the power saving state in which power supply to the controller unit is stopped, the image forming apparatus requires a time of several seconds to several tens of seconds (sleep return time). When the sleep return time of the image forming apparatus is longer than the above-mentioned specific time, and if the image forming apparatus shifts to the power saving state, it cannot send back a response to the communication partner device within the specific time.